1. Field of the Invention
The present invention relates to a vehicle including a supercharger.
2. Description of the Related Art
A supercharger has been used in order to improve the engine power in vehicles such as snowmobiles and four-wheel buggies. U.S. Pat. No. 7,198,127 discloses a snowmobile including a turbo-type supercharger that utilizes the energy of the exhaust gas from the internal combustion engine. U.S. Patent Application Publication No. 2007/0102215 discloses a snowmobile including a mechanical supercharger that is driven by the crankshaft of the internal combustion engine.
A turbo-type supercharger utilizes the energy of the exhaust gas, and when it is used in an off-road vehicle such as a snowmobile or a four-wheel buggy, the responsiveness is poor in the low- to mid-speed range where the energy of the exhaust gas is small. That is, in the low- to mid-speed range, the effect of the turbo-type supercharger for enhancing the engine power does not respond well to the throttle control. Moreover, the use of hot exhaust gas necessitates an advanced thermal management in the turbo-type supercharger and the engine room.
With a supercharger that is driven by the crankshaft, a vehicle that is normally used at a high engine speed, such as a snowmobile, will have an unnecessarily high supercharging pressure at a low speed. The need to control the supercharging pressure so that the supercharging pressure will not be too high leads to a complicated structure. An off-road vehicle such as a snowmobile or a four-wheel buggy is sometimes used under harsh environments such as subfreezing temperatures. When using a supercharger that is driven by the crankshaft, the load on the crankshaft is increased by the power used to drive the supercharger. Therefore, when starting the engine with a starter motor, it is necessary to provide a large power to the crankshaft, and it is thus necessary to provide a larger starter motor.